It is said that Cresselia is locked in a cosmic struggle with Darkrai, and that towards the end of every lunar month, with her last dying gasps of strength, she sacrifices herself in a magical and fatal dance so that Jirachi and the Sun can drive away the darkness. It is this cycle of death and rebirth which gives the most life to her cult, which mourns on a monthly basis when the moon wanes to nothing, then celebrates when a crescent appears anew.
Some of Cresselia's followers, whipped into a selfless frenzy by prayer, or hoping to save loved ones from illness or critical injuries, attempt to perform the Lunar Dance as well. Although it is re-enacted every month in this pokemon's temples, only Cresselia can perform the lunar dance properly; these re-enactors are not injured, and many cynical priests have considered it lucky that Cresselia did not use a fang, gun, or sword!
Yet Cresselia is seen as the Earth's protector even when alive, although her followers rarely pay it any heed until the holidays which mark her death; in their defense, while the holidays of other faiths come once a year, the festival of her sacrifice happens monthly. She is said to wrap the world in a giant, cosmic Reflect and Light Screen which together protect the earth from asteroids, ultraviolet rays, and other potential cataclysms from the stars. Before modern astronomy, this was taken literally; artists and theologians alike portrayed the world as protected by Cresselia's brilliant, looping pink wings, as though Earth was a ringed planet. Today, Cresselia's followers typically associate these screens with the atmosphere and the Moon's gravity, which do protect our world from asteroids and meteors, and fear catastrophe only during the time of the new moon.